Start by renting gear before you invest - honestly it's the best way to avoid ending up with skis that don't suit you. Near Grenoble you've got some good resorts with rentals, so take advantage and try different styles (classic vs skate) to see what you actually like.
For the basics, you can really get started without breaking the bank. A full rental set costs around 15-25€ per day, so if you do 3-4 outings before buying you'll have a solid idea. If you're set on buying after that, budget for basics around 300-500€ for skis + poles + secondhand or entry-level boots - it's nowhere near as pricey as other winter sports.
The real costs come later: proper clothing (base layer, thermal pants, windbreaker) that you can actually reuse for other winter activities anyway, and access to the slopes. But the basic gear itself isn't expensive to start with. What's your style anyway - do you want to stick to groomed trails doing classic, or try skate which is more dynamic?